Click on the item in the Finder’s sidebar with the house icon and verify that you are able to write to this folder in the Ownership & Permissions section of the Get Info window, and that it isn’t locked; if it is already set this way and you get that error, open the Terminal in the /Applications/Utilities/ folder and run the following:

mkdir ~/.Trash

If you get a message stating that the folder exists, run the following:

sudo chown $UID ~/.Trash
chmod u+rwx ~/.Trash

The first command in the second set will prompt you for your administrator password; nothing will appear in the Terminal window while it is being typed. In either case, click on the Finder icon in the Dock with the Control and Option keys pressed, and relaunch it.

There are many reasons why you’d want to reset your MacBook Air to factory settings. Perhaps your Mac is showing just a too much little lag. Maybe you want to reset for better overall performance, are thinking of giving away or selling your MacBook after you purchase or receive the latest Mac model. For whatever reason, you need to set your Mac back to its factory defaults.

Since our Macs hold so much of our personal and private data, it’s imperative to clean out our machines when selling or giving away our favorite older Macs. And it’s particularly useful for the new user to have a nice clean machine that’s returned to its native factory state.

At the command line, environmental variables are defined for the current shell and become inherited by any running command or process. They can determine anything from the default shell, the PATH, the users home directory, to the terminal emulation type, current working directory, where a history file is located, language and localization settings, and going further to include shell variables, which include everything from customizations to the bash prompt, colorized ls output, and changes to terminal appearance, to aliases, and much more.

Let’s walk through how to list environment and shell variables, and then how to set and add new environment variables at the command line of Mac OS X.

Displaying Current Environment & Shell Variables in Mac OS X

To quickly get a list of environmental variables, you can use the following command:

printenv

If you want to see a complete list of shell variables, the ‘set’ command can be issued as well:

set

The output of these commands can be lengthy so you may wish to pipe the output through the less or more commands.Lire la suite…

Introduction

In this tutorial, we will go over how to use Apache JMeter to perform basic load and stress testing on your web application environment. We will show you how to use the graphical user interface to build a test plan and to run tests against a web server.

JMeter is an open source desktop Java application that is designed to load test and measure performance. It can be used to simulate loads of various scenarios and output performance data in several ways, including CSV and XML files, and graphs. Because it is 100% Java, it is available on every OS that supports Java 6 or later.

Prerequisites

In order to follow this tutorial, you will need to have a computer that you can run JMeter on, and a web server to load test against. Do not run these tests against your production servers unless you know they can handle the load, or you may negatively impact your server’s performance.

You may adapt the tests in this tutorial to any of your own web applications. The web server that we are testing against as an example is a 1 CPU / 512 MB VPS running WordPress on a LEMP Stack, in the NYC2 DigitalOcean Datacenter. The JMeter computer is running in the DigitalOcean office in NYC (which is related to the latency of our tests).

Please note that the JMeter test results can be skewed by a variety of factors, including the system resources (CPU and RAM) available to JMeter and the network between JMeter and the web server being tested. The size of the load that JMeter can generate without skewing the results can be increased by running the tests in the non-graphical mode or by distributing the load generation to multiple JMeter servers. Lire la suite…

Database tuning is an expansive topic, and this guide covers only the basics of editing your MySQL configuration. Large MySQL databases can require a considerable amount of memory. For this reason, we recommend using a high memory Linode for such setups.

The steps in this guide require root privileges. Be sure to run the steps below as root or with the sudo prefix. For more information on privileges see our Users and Groups guide.

Tools That Can Help Optimize MySQL

In order to determine if your MySQL database needs to be reconfigured, it is best to look at how your resources are performing now. This can be done with the top command or with the Linode Longview service. At the very least, you should familiarize yourself with the RAM and CPU usage of your server, which can be discovered with these commands:

MySQLTuner offers suggestions regarding how to better the database’s performance. If you are wary about updating your database on your own, following MySQLTuner’s suggestions is one of the safer ways to improve your database performance.

Tuning MySQL

When altering the MySQL configuration, be alert to the changes and how they affect your database. Even when following the instructions of programs such as MySQLTuner, it is best to have some understanding of the process.

The file you are changing is located at /etc/mysql/my.cnf.

Prior to updating the MySQL configuration, create a backup of the my.cnf file:

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cp /etc/mysql/my.cnf ~/my.cnf.backup

Best practice suggests that you make small changes, one at a time, and then monitor the server after each change. You should restart MySQL after each change:

For systems without systemd:

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systemctl restart mysqld

For distributions which don’t use systemd:

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service mysql restart

When changing values in the my.cnf file, be sure that the line you are changing hasn’t been commented out with the pound (#) prefix.

key_buffer

Changing the key_buffer allocates more memory to MySQL, which can substantially speed up your databases, assuming you have the memory free. The key_buffer size should generally take up no more than 25 percent of the system memory when using the MyISAM table engine, and up to 70 percent for InnoDB. If the value is set too high, resources are wasted.

According to MySQL’s documentation, for servers with 256MB (or more) of RAM with many tables, a setting of 64M is recommended. Servers with 128MB of RAM and fewer tables can be set to 16M, the default value. Websites with even fewer resources and tables can have this value set lower.

max_allowed_packet

This parameter lets you set the maximum size of a sendable packet. A packet is a single SQL state, a single row being sent to a client, or a log being sent from a master to a slave. If you know that your MySQL server is going to be processing large packets, it is best to increase this to the size of your largest packet. Should this value be set too small, you would receive an error in your error log.

thread_stack

This value contains the stack size for each thread. MySQL considers the default value of the thread_stack variable sufficient for normal use; however, should an error relating to the thread_stack be logged, this can be increased.

thread_cache_size

If thread_cache_size is “turned off” (set to 0), then any new connection being made needs a new thread created for it. When the connections disengage the thread is destroyed. Otherwise, this value sets the number of unused threads to store in a cache until they need to be used for a connection. Generally this setting has little affect on performance, unless you are receiving hundreds of connections per minute, at which time this value should be increased so the majority of connections can be made on cached threads.

max_connections

This parameter sets the maximum amount of concurrent connections. It is best to consider the maximum amount of connections you have had in the past before setting this number, so you’ll have a buffer between that upper number and the max_connections value. Note, this does not indicate the maximum amount of users on your website at one time; rather it shows the maximum amount of users making requests concurrently.

table_cache

This value should be kept higher than your open_tables value. To determine this value use:

As with all relational databases, MySQL can prove to be a complicated beast, one that can crawl to a halt at a moment’s notice, leaving your applications in the lurch and your business on the line.

The truth is, common mistakes underlie most MySQL performance problems. To ensure your MySQL server hums along at top speed, providing stable and consistent performance, it is important to eliminate these mistakes, which are often obscured by some subtlety in your workload or a configuration trap.

Luckily, many MySQL performance issues turn out to have similar solutions, making troubleshooting and tuning MySQL a manageable task.

Here are 10 tips for getting great performance out of MySQL.

MySQL performance tip No. 1: Profile your workload

The best way to understand how your server spends its time is to profile the server’s workload. By profiling your workload, you can expose the most expensive queries for further tuning. Here, time is the most important metric because when you issue a query against the server, you care very little about anything except how quickly it completes.

The best way to profile your workload is with a tool such as MySQL Enterprise Monitor’s query analyzer or the pt-query-digest from the Percona Toolkit. These tools capture queries the server executes and return a table of tasks sorted by decreasing order of response time, instantly bubbling up the most expensive and time-consuming tasks to the top so that you can see where to focus your efforts.

Workload-profiling tools group similar queries together, allowing you to see the queries that are slow, as well as the queries that are fast but executed many times.

Introduction

Full-text search, or FTS, is a technique used by search engines to find results in a database. You can use it to power search results on websites like shops, search engines, newspapers, and more.

More specifically, FTS retrieves documents that don’t perfectly match the search criteria. Documents are database entities containing textual data. This means that when a user searches for « cats and dogs », for example, an application backed by FTS is able to return results which contain the words separately (just « cats » or « dogs »), contain the words in a different order (« dogs and cats »), or contain variants of the words (« cat » or « dog »). This gives applications an advantage in guessing what the user means and returning more relevant results faster.

Technically speaking, database management systems (DBMS) like MySQL usually allow partial text lookups using LIKE clauses. However, these requests tend to underperform on large datasets. They’re also limited to matching the user’s input exactly, which means a query might produce no results even if there are documents with relevant information.

Using FTS, you can build a more powerful text search engine without introducing extra dependencies on more advanced tools. In this tutorial, you will use MySQL 5.6 to query a database using full-text search, then quantify the results by their relevance to the search input and display only the best matches.

Introduction

While many users need the functionality of a database management system like MySQL, they may not feel comfortable interacting with the system solely from the MySQL prompt.

phpMyAdmin was created so that users can interact with MySQL through a web interface. In this guide, we’ll discuss how to install and secure phpMyAdmin so that you can safely use it to manage your databases from an Ubuntu 16.04 system.

Prerequisites

Before you get started with this guide, you need to have some basic steps completed.

We’re also going to assume that you’ve completed a LAMP (Linux, Apache, MySQL, and PHP) installation on your Ubuntu 16.04 server. If this is not completed yet, you can follow this guide on installing a LAMP stack on Ubuntu 16.04.

Finally, there are important security considerations when using software like phpMyAdmin, since it:

Communicates directly with your MySQL installation

Handles authentication using MySQL credentials

Executes and returns results for arbitrary SQL queries

For these reasons, and because it is a widely-deployed PHP application which is frequently targeted for attack, you should never run phpMyAdmin on remote systems over a plain HTTP connection. If you do not have an existing domain configured with an SSL/TLS certificate, you can follow this guide on securing Apache with Let’s Encrypt on Ubuntu 16.04.

Once you are finished with these steps, you’re ready to get started with this guide.

Introduction

MySQL comes with a handy little diagnostic tool called mysqlslap that’s been around since version 5.1.4. It’s a benchmarking tool that can help DBAs and developers load test their database servers.

mysqlslap can emulate a large number of client connections hitting the database server at the same time. The load testing parameters are fully configurable and the results from different test runs can be used to fine-tune database design or hardware resources.

In this tutorial we will learn how to use mysqlslap to load test a MySQL database with some basic queries and see how benchmarking can help us fine-tune those queries. After some basic demonstrations, we will run through a fairly realistic test scenario where we create a copy of an existing database for testing, glean queries from a log, and run the test from a script.

The commands, packages, and files shown in this tutorial were tested on CentOS 7. The concepts remain the same for other distributions. Lire la suite…